One of the most important pathways available to organisms for the detoxication of potentially harmful chemicals is via reaction with glutathione. Among the numerous transformations involving alkylating reactions of glutathione, its reaction with epoxides was selected for thorough examination. This choice was dictated by our interest in the mechanism of biosynthesis of epoxides and the implication of these compounds as direct acting toxic agents. The project consisted of two phases, a chemical and an enzymatic component, for which the following objectives were defined: 1) develop methodology for the study of glutathione reactions with epoxides; 2) establish the stereochemical fate of these transformations; 3) elucidate the mechanism(s) of the enzyme catalyzed reaction of glutathione with epoxides. The first objective was accomplished with the development of methods which allow the preparation of diastereomerically pure glutathione conjugates as well as sensitive methods for the analysis of such compounds. The stereochemical course of the epoxide ring opening step was established with the aid of optically pure epoxides. This knowledge was translated into stereochemical profiles whereby diastereomer identification on a reversed-phase liquid chromatography system became possible. Experiments with various epoxide substrates and hepatic glutathione transferases from the little skate and the rat showed remarkable stereochemical consistency. In both cases, a majority of the purified enzymes showed a high preference for attack-addition of thiol at the R-carbon on the epoxide ring. Other enzymes showed the opposite preference, i.e. addition to the S-carbon. A mechanism was postulated to explain the stereoselectivity of this enzymatic transformation and based on this mechanism a model was proposed for the active site geometry of three glutathione transferases. The use of stereochemical profiles as a way of assessing differences, or similarities, among glutathione transferases is currently being explored.